Indirect Estimation of Design Flood in Urbanized River Basins Using a Distributed Hydrological Model

Abstract

A method for indirect estimation of design flood in poorly gauged urbanized river basins by using distributed hydrological modelling is presented. It is based on the critical flood design criterion that maximizes peak flow for a given return period by transforming precipitation of depth duration frequency curve into runoff. The indirect method is compared against the direct method based on regional approach and index flood estimation. This paper shows that the direct method significantly underestimates design flood in case discharge measurements are strongly affected by artificial alteration of water courses with possible catastrophic consequences in terms of loss of life and damage to property when the cause of alteration would be removed. Moreover, the use of a spatially distributed model allows taking into account the heterogeneity that generally characterizes river basins with an high degree of urbanization. The presented indirect method provides a design hydrograph that is useful for those cases in which design discharge only is not sufficient for designing or planning purposes.